1. Field of the Invention
The present invention relates to high solids coating compositions, and more particularly, to high solids coating compositions containing acrylic polymers.
2. Brief Description of the Prior Art
Acrylic polymers are well known in the art as resinous binders for coating compositions. The acrylic polymers provide for hardness, gloss and exterior durability in the resultant coating making them particularly desirable as finishes for automobiles. The polymers may be thermoplastic or thermosetting in nature. For thermosetting polymers, the alpha, beta-ethylenically unsaturated monomer component usually includes a functional monomer such as a hydroxyl-containing monomer and the resulting polymer is combined with a curing agent such as a polyisocyanate or aminoplast resin to form a curable or thermosetting composition.
The compositions can be formulated with high molecular weight acrylic polymers. However, such polymers require the presence of relatively high amounts of organic solvent to reduce the viscosity of the polymer sufficiently for coatings applications. The high percentage of organic solvent results in air pollution problems. To avoid these problems, there has been a trend in the coatings industry to develop so-called high solids coatings which contain relatively low amounts of organic solvent. The polymers in such high solids compositions are of relatively low molecular weight so that the polymer will have a low viscosity and will not need much organic solvent for coatings application.
Unfortunately, low molecular weight acrylic polymers do not provide coatings with physical and chemical properties as good as coatings prepared from higher molecular weight acrylic polymers. In commerical practice a compromise is usually made between the molecular weight of the acrylic polymer and the solids content of the coating composition. Also, many of the high solids acrylic polymer coating compositions have a yellow cast when applied as a clear coat as is often done in automotive coatings when a clear coat is applied over a colored or pigmented basecoat.